A surface mount technology (SMT) is a method for mounting electronic components on the surface of a printed circuit board. The surface mount technology is capable of automatically fabricating small-sized, reliable, high-density and cost-effective electronic products. Generally, the solder paste printing pattern for the surface mount technology is defined by the apertures of a stencil. In addition, solder paste may pass through the apertures of the stencil to corresponding bonding pads of the printed circuit board. In other words, the stencil is a very important part of the surface mount technology. Moreover, the tension of the stencil should be maintained at a certain level. By the tension, the solder paste printed on the bonding pads will not stain the stencil, and thus the solder paste will not be detached. That is, if the tension is insufficient, the printing quality is deteriorated.
FIG. 1 is a schematic exploded view illustrating a conventional assembled solder paste printing structure for printing solder paste on a printed circuit board. As shown in FIG. 1, the conventional assembled solder paste printing structure 9 comprises a fixing frame 91, a hollowed-out rectangular stretching net 92, and a steel plate 93. The steel plate 93 is rectangular, and has a rectangular solder paste printing region 931 and a fixing region 932. The four sides of the solder paste printing region 931 are surrounded by the fixing region 932. The solder paste printing region 931 comprises plural apertures 9311 for providing solder paste. The fixing region 932 is attached on inner edges of four sides of the stretching net 92. Consequently, equal pulling forces are applied to the outer edges of the four sides of the stretching net 92 to outwardly tighten the stretching net 92 in order flatten the steel plate 93. Then, the steel plate 93 is fixed in the clamping slots 911 at the four sides of the fixing frame 91.
A process of using the conventional assembled solder paste printing structure 9 will be illustrated as follows. Firstly, a printed circuit board (not shown) is fixed on a platform (not shown) of a machine (not shown) horizontally. Then, the fixing frame 91 of the conventional assembled solder paste printing structure 9 is fixed on the machine. Then, the steel plate 93 of the conventional assembled solder paste printing structure 9 is aligned with and placed on the printed circuit board. Then, solder paste is scraped across the solder paste printing region 931 of the steel plate 93, so that the solder paste is provided within the apertures 9311 of the steel plate 93 and adhered on the printed circuit board. Afterwards, the conventional assembled solder paste printing structure 9 is removed. Consequently, plural solder paste spots are spread on the printed circuit board, and the printed circuit board is further processed.
However, the use of the conventional assembled solder paste printing structure still has some drawbacks. For example, since the tension is not uniformly and properly distributed on the rectangular steel plate, the printing quality is usually unsatisfied. Moreover, after the conventional assembled solder paste printing structure has been used for a certain time period, the tension of the rectangular steel plate is possibly destroyed and impaired. Moreover, since the conventional assembled solder paste printing structure cannot be disassembled, the conventional assembled solder paste printing structure fail to match various printed circuit boards. Under this circumstance, the assembling process is complicated, and the assembling cost is increased.
Therefore, there is a need of providing an improved stencil assembly structure in order to eliminate the above drawbacks.